Polyacetal resins are well known and have been used in a number of end-use applications as an engineering resin due to its excellent physical and chemical characteristics (such as mechanical electrical characteristics, as well as its resistance to chemicals or heat. As the field in which a polyacetal resins are utilized expand, however, more stringent and/or special properties for polyacetal resins are needed.
One of such special properties is improved weathering (light) resistance. Particularly, exterior automotive trims or components of electric appliances or business machines which are made of a polyacetal resin tend to determinate when exposed to "weathering" conditions, such as sunlight, wind and rain, fluorescent lamps or contact with the atmosphere. weathering of polyacetal resins is manifested in discoloration, disappearance of gloss with reduced surface smoothness, a reduction in the mechanical properties and crack generation on the surface of molded articles of the resin. In order to inhibit these troubles, it has been proposed to improve the weathering resistance of polyacetal resins by the addition of various stabilizers.
Although some improvement is achieved by incorporating stabilizers in polyacetal resins according to the prior art, molded articles polyacetal resin do not always exhibit satisfactory results in terms of appearance (crack or gloss) and/or mechanical properties after prolonged exposure to sunlight (ultraviolet light). Therefore, polyacetal resins exhibiting further improvements in weather stability is required in many cases.
In order to fulfill this requirement, it has been attempted to increase the amount of the weathering stabilizer added to the polyacetal base resins. However, merely increasing the amount of the stabilizer results in only a limited improvement. In addition, excessive amounts of stabilizer is problematic or disadvantageous in that the mechanical properties (such as tensile strength or flexural strength) of the polyacetal resin are reduced and the stabilizer may "bleed" into the surfaces of molded articles. In addition, excess the stabilizer tends to adhere or build-up on the surfaces of molds (i.e., so-called-mold deposits) during molding of the resin. This invention affects the dimensional accuracy and/or appearance of the resulting molded article. As a result mold must be cleaned more frequently thereby lowering molding efficiency that other various troubles such as a poor appearance of a molding due to bleeding of a stabilizer occur more often.
The present invention relates to a weather-resistant polyacetal resin composition comprising
(A) a polyacetal base resin, PA1 (B) between 0.01 to 5% by weight (based on the whole composition) of a weathering (light) stabilizer, and PA1 (C) between 0.01 to 10% by weight (based on the whole composition) of an acrylic terminated polyester oligomer.
Further aspects of this invention will become more clear after consideration is given to the following detailed description thereof.